(a) Field of the Invention
The present invention relates to a process for the production of a thermo-developable type diazo copying material which comprises combining a diazonium salt, a coupler and a heat fusible color assistant with fine particles of a specified hydrophobic resin; dividing this into two aqueous liquids of diazonium salt-resinous fine particle system and coupler system; and coating them onto a substrate.
(b) Description of the Prior Art
As the processes for the production of thermo-developable type diazo copying materials (or diazo system heat sensitive recording materials) there have hitherto been well known the following ones: a process that comprises coating an aqueous solution or dispersion consisting essentially of a diazonium salt, a coupler and an alkali generating agent such as urea, sodium trichloroacetate or the like on a substrate such as paper, plastic film or the like and drying, (2) a process that comprises using a heat fusible color assistant such as a high fatty acid amide in place of the alkali generating agent in the process disclosed in the preceding (1), (3) a process that comprises using the coupler of the preceding process (2) encapsulated with a hydrophobic substance such as resin, (4) a process that comprises coating and drying an organic solvent dispersion consisting essentially of a diazonium salt (or coupler) and a hydrophobic resin onto a substrate and thereafter coating and drying an organic solvent or aqueous solution or dispersion consisting essentially of a coupler (or diazo compound) further thereon, and the like.
However, the copying material obtained by the process (1), which is required to be developed at a high temperature of 150.degree. to 200.degree. C., must use a highly thermostable diazonium salt that is unfavorable for the formation of a high density image and further is in need of a high temperature and highly accurate heating equipment. The copying material obtained by the process (2), which may be developed at a low temperature unlike that obtained by the process (1), can surely produce a high density image but is defective in that the preservability of the copying material per se (which is referred to as "raw preservability" hereinafter) is inferior. The copying material obtained by the process (3), wherein the coupler is encapsulated with a hydrophobic substance, can surely ameliorate the defect inherent in the copying material obtained by the process (2) but it is difficult to obtain a high density image at a low developing temperature. On the other hand, the process (4) is defective in that the production cost becomes very expensive because, due to the use of an organic solvent, uniform permeation into a paper substrate is prevented so that stable coating is hindered, a special and accurate coating means is needed and further a means for recovering the organic solvent used is needed, and further that there is a possibility of incurring the danger of workers being poisoned by the organic solvent or causing a fire.